Method of and means for applying corrosion inhibiting coating



United States Patent Office 3,300,333 Patented Jan. 24, 1967 3,300,333METHOD OF AND MEANS FOR APPLYING CORROSION INHIBITING COATING Mary AnnePage, Minneapolis, Minn., assignor to Minnesota Mining and ManufacturingCompany, St. Paul,

Minn., a corporation of Delaware No Drawing. Filed May 27, 1963,Ser. No.283,564

6 Claims. (Cl. 117120) This invention relates to a novel method of andmeans for applying an extremely thin but effective corrosion-inhibitingcoating to metal surfaces. It particularly relates to a simple means forthe commercial applications of such coatings.

The manufacturers of sheet metal have long been faced with a problem ofcorrosion inhibition. A typical situation exists in a copper mill, wherecupreous strips on the order of .030 inch thick and up to feet wide areproduced and wound convolutely into coils several hundred feet long.Such coils are then sent to the plant of a copper fabricator where theymay be further reduced in thickness and/ or formed into finishedproducts. The lag between the time when the copper leaves the mill andthe time when it is utilized by the fabricator may be six months ormore.

Sheet copper is a strikingly attractive raw material but it is subjectto numerous types of corrosion. It is deleteriously affected by salt,for example, and a fingerprint which is inadvertently left on a coppersurface often proves to be the site of destructive corrosive attack. Itis also discolored unattractively and irregularly by exposure to theatmosphere, especially when hydrogen sulfide is present. Before afabricator can use discolored or corroded copper sheets, he is compelledto remove the blemish, usually by abrasion, generally simultaneouslyremoving adjacent sound metal. The process is inconvenient, expensive,and wasteful, and it is thus common commercial practice to return sheetcopper to the supplier if it contains serious visually detectabledefects.

In an attempt to reduce the quantity of cupreous sheet metal which isreturned, mills have resorted to numerous techniques to limit corrosion,none of which is universally satisfactory. For example, oil or greasereduces corrosion slightly, but it is messy and inconvenient to remove.Where the oil-in-water emulsion of rolling lubricant is allowed toremain, corrosion is reduced very little and irregular stains oftenappear on the metal strip.

Where the copper sheet is annealed before leaving the mill, theannealing scale is ordinarily removed by passing the sheet through apickling tank. Subsequent to this operation the sheet may be passedthrough a tank containing acidified sodium chromate and variouscatalysts to apply a chromate conversion coating to the surface.Although this process employs inexpensive raw materials and is fairlyeffective, the resulting surface is often nonuniform because of unevenwetting, the high water marks themselves often providing the site forsubsequent corrosion. In addition, the chromate conversion operationchanges the color of the copper and increases the difficulty of furtherthickness reduction. Further, although this process is well-suited tooperations where a wet scale removal treatment of the annealed copper isalready necessary, it is expensive and inconvenient when the copperwould not ordinarily be subjected to such an operation.

It has also been proposed to minimize the tarnishing of copper sheets byWrapping them in paper or cloth impregnated with a vapor phase corrosioninhibitor. Al-

though theoretically sound, this process is inconvenient, expensive, andhas not gained very wide acceptance.

In some instances fabricators have coated cupreous products, such asplanters, teakettles, or copper-bottomed pans, with lacquer, but thelacquer itself may discolor, and frequently tarnish may appearunexplainably and spread beneath the lacquer, which then must beremoved, at considerable inconvenience.

It is known to apply a corrosion inhibiting compound to a metal surfaceand then to rub the treated surface with a cloth, and it would not besurprising to find that a cloth could be periodically dipped in asolution of corrosion inhibitor and rubbed over a metal surface to leavea protective coating. Commercially, however, such procedures arecontraindicated, since solvent removal is hazardous, extra equipment isneeded, and it has been supposed that frequent retreatment of the clothwould be necessary and that degree of corrosion resistance would varywidely. Insofar as I am aware, then, no one has given any seriousconsideration to frictionally transferring a solvent-freecorrosion-inhibiting compound from a treated fibrous structure to ametal workpiece.

I have now found a novel, simple, and unexpected means for and method ofimparting excellent corrosion resistance to cupreous and other metalsurfaces. The appearance of the surface remains unchanged, and treatedsheet can be readily rolled, soldered, or lacquered after only theconventional degreasing operation. The method of my invention isparticularly adapted to industria plants, where unskilled persons areable to obtain consistently good results for extended periods of time.

In accordance with my invention I apply to a metal surface an extremelythin layer of an organic corrosioninhibiting compound which is capableof becoming bound to the metal by chemisorption.

In applying the corrosion-inhibiting compound, I employ a rotary porousfibrous rubbing element, such as a buffing wheel, which contains at itsworking surface and for a substantial distance inwardly therefrom on theorder of 0.005 to 0.1 part of a solvent-free corrosion inhibitingcompound per part of fiber. I have found that such a rubbing element maybe used continuously through-out an 8-hour shift with no detectable wearand with only an unimportant decrease in the degree of corrosionresistance imparted. Even after treating thousands of lineal feet ofmetal, the treated fibrous rubbing element is readily restored to fullfunctional efficiency by lightly dressing or combing the surface,thereby removing any matted fibers and oxidized metal which may beadhering thereto. The rate of wear, is in fact, so infinitesimal thatthe amount of corrosion-inhibiting compound transferred to the metalsurface has been calculated to have an effective thickness far below 500Angstrom units, or less than one-tenth the wave length of the lowerlimit of the visible light spectrum.

Among the attractive commercial aspects of my novel process are thefacts that it can be put into effect very quickly and easily in almostany metal strip finishing line, that the equipment is simple,inexpensive, and compact, and that there is very little criticality ofadjustment, and that, as indicated, the treated fibrous rubbing elementneeds only-the most perfunctory attention. The process is entirely dry,involving no immersion tanks, drying facilities or expensive andhazardous solvents. Cost of the treating materials themselves is almostinsignificant, and the saving on metal which must be refinished orreturned to the mill overwhelmingly outweighs any costs resulting fromuse of the process.

My invention will be further illustrated by means of severalnon-limiting examples set forth below in which all parts are by weightunless otherwise noted.

Example Three twenty-ply sections of /92 muslin (No. 2 sheeting, 4 sq.yds./ 1b.), each having a 9 inch diameter, 1% inch centerhole, and fourrows of concentric machine sewing /2 inch apart, were immersed in andallowed to absorb all of a solution of 6.5 g. of alpha-mercaptostearicacid in 400 ml. of acetone. The sections were then removed from thesolution and slowly rotated until the acetone evaporated. The averagelevel of treatment thus attained was 2.24 g. of alpha-mercaptostearicacid per sq. yd. of cloth, or 2% of the weight of the cloth. The threesections were then axially ganged between a pair of /2 inch diameterside plates and driven at 1700 r.p.m. Three 1" x 3 x copper samples,previously cleaned abrasively, Were now treated by hand, the operatorquickly moving the piece so that one entire major surface contacted theperiphery of the wheel. Three identical copper samples were similarlybuffed with a control wheel which contained no alpha-mercaptostearicacid but was otherwise identical. These six samples, all identical inappearance, were exposed to an atmosphere of 100 p.p.m. H 8 and 100%relative humidity at room temperature for 2 hours. The control sampleswere stained a dark blue-green and red whereas the test samples showedonly a slight brown tarnish around the edges.

Example 2 Three muslin'sections of the type described in Example 1 wereimmersed in and allowed to absorb all of a solution of 7 g. of NalcamineG-39M corrosion inhibitor (3. semi-solid mixture of compounds having thestructure:

/NCH2 RC N-CH2 CHzCHzNHz wherein R is a l7-carbon alkyl chain having oneor two double bonds) in 400 ml. of acetone and slowly rotated whilebeing allowed to dry. The average level of treatment thus attained was2.41 g./sq. yd. of fabric or 2.16% of the weight of the cloth. Thesections were then mounted and driven as in Example 1 and used to treat1" x 3" samples of sheet copper, brass and steel as in Example 1. Thetreated samples were then tested by placing 5 drops of a 0.5% sodiumchloride solution on the surface and timing the appearance of the firsttarnish or rust. The results were as follows:

Minutes Untreated copper 22 Treated copper 2500 Untreated brass 31Treated brass 495 Untreated steel 5 Treated steel 18 Example 3 Threemuslin sections, as in Example 1, were immersed in and allowed to absorball of a solution of 6 g. of nonylphenoxyacetic acid (a viscouscorrosion-inhibiting liquid obtained from Geigy Co.) in 400 ml. ofacetone and rotated until the acetone evaporated. The average level oftreatment thus attained was 2.07 g./sq. yd. of fabric or 1.85% of theweight of the cloth. This wheel was used as in Example 1 to treatsamples of copper, brass and steel, which were then tested for corrosionresistance as in Example 2. The results were:

Minutes Untreated copper 22 Treated copper 360 Untreated brass 31Treated brass 870 Untreated steel 5 Treated steel 90 Example 4 Threemuslin sections, as in Example 1, were immersed in and allowed to absorball of a solution of 10 g. of cyclohexylamine nitrite in 500 ml. ofmethanol and 4 rotated while being allowed to dry. The average level oftreatment thus attained was 3.45 g./sq. yd. of the fabric or 3.1% of theweight of the cloth. This wheel was used as in Example 1 to treatsamples of copper and brass, which were then tested for corrosionresistance as in Example 2. The results were:

Minutes Untreated copper 22 Treated copper 360 Untreated brass 31Treated brass 165 Example 5 Three muslin sections, as in Example 1, wereimmersed in and allowed to absorb all of a solution of 10 g. ofoctadecylamine in 500 ml. of acetone and rotated while being allowed todry. The average level of treatment thus attained was 3.45 g./sq. yd. ofthe fabric or 3.1% of the weight of the cloth. This wheel was used, asin Example 1, to treat copper, brass, steel and silver samples. Thecopper, brass and steel samples were then tested for corrosionresistance as in Example 2. The results were:

Minutes Untreated copper 22 Treated copper 3700 Untreated brass Treatedbrass Untreated steel 5 Treated steel 18 The silver samples were testedin an H S atmosphere, as in Example 1, for six hours. After thisexposure the control sample was tarnished -to a brown color whereas thetreated sample remained bright silver.

Example 6 A nonwoven web (3.47 sq. yd./lb.) for-med from scrap cottonthreads bonded with regenerated viscose xanthate was uniformly rollcoated with g./square yard (wet weight) of a 5% solution ofoctadecylmercaptan in toluene. The web was then dried and 12 inchdiameter discs having a 1% inch centerhole were died therefrom, thelevel of treatment thus attained being 5 -g./sq. yd. of the fabric or3.8% of the weight of the cloth. Twelve such discs were stapled togetherto form a section and a Wheel was made from two usch sections. Thiswheel was used, as in Example 1, to treat two samples of copper, whichwere then exposed to an H S atmosphere, as in Example 1, for two hours.An untreated control sample became tarnished to a dark blue-green andred color whereas the treated samples remained untarnished.

Example 7 Fifty 9-inch diameter discs having a l flt-inch centerholewere died from a web (5.6 sq. yd./lb.) of nonwoven cotton fibers lightlybonded with Hycar 1571 butadienezacrylonitrile copolymer latex, andaxially ganged. The resultant wheel was immersed in and allowed toabsorb all of a solution of 10 g. of octadecylmercaptan in 800 ml. ofacetone and then rotated while being allowed to dry. The level oftreatment thus attained was 4.15 g./sq. yd. of the fabric or 5.1% of theweight of the cloth. This wheel was mounted :between side plates andused, as in Example 1, to treat two samples of copper which were thenexposed to an atmosphere of H 8, as in Example 1, for 2 hours. A controlsample became tarnished with :a dark blue-green and red color while thetreated samples remained as bright copper.

Example 8 A 9-inch diameter lambs wool 'bonnet approximately 1 inchthick was immersed in and allowed to absorb all of a solution of 7 g. ofoctadecylmercapta-n in 200' ml. of heptane and then dried. The level oftreatment was approximately 0.11 g./cu. in. of lambs wool. This bonnetwas then mounted on the head of a portable disc sander driven at 1500r.p.m. and used to treat an 8 x 10 inch copper panel. After testing byexposure to an H 8 atmosphere, as in Example 1, a control sample ofcopper became darkly tarnished whereas the treated panel showed no signsof tarnish.

Example 9 Two l7-inch diameter Jackson Airway buff sections having a7-inch centerhole, each made from 3.89 square yards of 86/93 count jeanscloth (2.6 sq. yd./lb were immersed in and allowed to absorb all of asolution of 9 g. of alpha-mercaptosteric acid in 600 ml. of acetone androtated while being allowed to dry. This gave a level of treatment of2.31 g./sq. yd. of the fabric or 1.32% of the weight of the cloth. Thetwo buff sections were then ganged between flanges, driven at 1700r.p.m., a-nd used to treat one-half of an 8 x 10 inch copper panel.After being exposed to an H S atmosphere, as in Example 1, for twohours, the untreated half of the copper panel showed a dark tarnishstreak whereas the treated half showed no discoloration.

Example 10 Jeans cloth webs having a 96/ 92 count (2.6 sq. yd./ lb.)were roll coated with 100 grams/square yard of various percentages ofoctadecylmercaptan (ODM) in toluene. Levels of treatment obtained wereas given in the following table:

Web Percent ODM in G. ODM/sq. yd. Percent ODM in olntion Cloth Forty9-inch diameter discs having l fit-inch centerholes were then stampedfrom each of the treated webs and six wheels formed. Each wheel was usedat 170 0 r.p.m. to treat two copper samples and two brass samples. Afterexposure in an H S atmosphere, as in Example 1, for two hours appearanceof the samples was as given in the The other set of samples was testedby placing on the metal a drop of a 0.5% sodium sulfide solution andtiming the appearance of the first discoloration. The results were asfollows:

Treatment Level in Brass Samples Copper Samples Wheel-Weight PercentControl (none) 30 sec... sec.

0.057 2 min 3 min.. 30 sec. 0.11-t 4 IXllIL, 30 sec 4 min, 40 sec.0.57-. 5 min., 30 see 5 min, 5 sec. 2.86 17 min, 20 secmin., 55 sec. 5.753 min 25 min.. 30 sec. 11.4 100 min, 30 sec 60 mm, 15 sec.

Example 11 A copper-bottom pan was buffed to a bright finish using aplai-n cloth buff and grease stick with tripoli. Lime dusting was usedto remove excess grease, and onehalf of the copper bottom was then colorbuffed using a cloth buff containing alpha-mercaptostearic acid.Fingerprints were deliberately placed on both halves. After 48 hoursexposure to air in an industrial laboratory, the fingerprints on theuntreated half had caused discoloration of the copper whereas on thetreated half all visible traces could be easily wiped off with tissue.This pan was then partially filled with water which was brought to aboil during 10 minutes and boiled for 20 minutes on a hot plate. Theuntreated half showed tarnish due to heat oxidation, whereas the treatedhalf maintained a good appearance except at the site of thefingerprints. Even after two more heating sequences the treated half wassuperior in appearance to the untreated half.

Example 12 A Jackson Airway cotton buff section having an outer diameterof 12 inches and a fluted /6. inch wide face was saturated with a 7 /2%solution of ODM in xylol and the solvent evaporated, leaving a depositof 4.3% octadeeylmercaptan based on the cotton cloth. This wheel wasthen mounted on an arbor, driven at 1750 r.p.m., and forced against theouter surface o-f a 7-foot x 4-inch copper band mounted on an inflatedauto tire and rotated at 4 r.p.m. This setup continuously transferredODM from the treating wheel to the surface of the copper band, anoperator continuously removing the ODM from the copper by alternatewiping with a solvent-dipped rag and a clean rag. From time to time theeffectiveness of the wheel was tested by forcing 1" x 3" copper andbrass coupons against the wheel, applying a drop of 0.5% Na s solutionto the thus-treated coupons, and noting the time required for a stain todevelop. Surprisingly, no stain developed within 60 minutes on eithertype of coupon until the treating wheel had run for yell over 10 hours.In contrast, untreated copper coupons stained in 30 seconds anduntreated brass coupons in 65 seconds.

After the treated wheel had been used for 12 hours, some matting anddiscoloration was noted, and ability to impart corrosion resistance wasdeclining. Combing the periphery with a conventional rake for buffingwheels quickly restored the original appearance and effectiveness.

The foregoing examples are intended to illustrate, but not to limit, thescope of my invention, and many variations will readily occur to thoseskilled in the art. To illustrate, there are numerous other organiccorrosioninhibiting compounds capable of being bound to a metallicsurface by chemisorption (i.e., having a functional group which reactswith the surface); thus the other mercaptans in the C C chain length,and compounds having metalreactive groups other than those I have namedmay be employed. Likewise the specific fibrous rotary rubbing elementmay take the form of a band entrained over one or more supportingwheels, although such embodiments tend to have shorted useful life aftertreatment than those of the preceding examples.

What I claim is:

1. The method of imparting corrosion-resistance to the surface of anormally corrodible cupreous metal which comprises contacting saidsurface with the working face of a rapidly rotating resilient rubbingelement while maintaining both said face and said surface in drycondition, said element comprising a porous structure formed fromorganic fibers uniformly provided at its working face and for asubstantial distance inwardly therefrom with a substance selected fromthe class consisting of organic compounds which are capable of beingbound to cupreous metal by chemisorption and which inhibit the corrosionof cupreous metal when applied to the surface thereof, the working faceof said element containing on the order of 0.005 to 0.1 part of saidsubstance per part of fiber, whereby said substance is frictionallytransferred to said surface to provide a uniform coating having athickness significantly less than the wave length of visible light.

2. The process of claim 1 wherein the organic compound is furtherselected from the class consisting of mercapto-aliphatic compoundshaving a chain length of about 16 to 22 carbon atoms, viscous alkylphenoxy carboxylic acids, and cyclohexylamine nitrite.

3. The process of claim 2 in which the cupreous metal is copper.

4. The process of claim 2 in which the cupreous metal is brass.

5. The method of imparting corrosion-resistance to the surface of anormally corrodible metal which comprises contacting said surface withthe working face of a rapidly rotating resilient rubbing element whilemaintaining both said face and said surface in dry condition, saidelement comprising a porous structure formed from organic fibersuniformly provided at its working face and for a substantial distanceinwardly therefrom with a substance selected from the class consistingof organic compounds which are capable of being bound to said metal bychemisorption and which inhibit the corrosion of said metal when appliedto the surface thereof, the working face of said element containing onthe order of 0.005 to 0.1 part of said substance per part of fiber,whereby said substance is frictionally transferred to said surface toprovide a uniform coating having a thickness significantly less than thewave length of visible light.

6. A flexible, soft, dry solvent-free rotative rubbing element formedfrom organic fibers, suitable for practicing the process of claim 1,said rubbing element being impregnated with 0.005 to 0.1 part per partof fiber of a corrosion inhibiting compound selected from the classconsisting of actadecyl mercaptan and alpha-mercapto stearic acid.

References Cited by the Examiner UNITED STATES PATENTS 2,257,750 10/1941Lincoln et al 252395 X 2,807,584 9/1957 Rushton 25291 2,896,242 7/1959Winch 15506 3,062,612 11/1962 Le Boucher. 3,117,012 7/1964 Alder et a11063 X RALPH S. KENDALL, Primary Examiner.

RICHARD D. NEVIUS, Examiner.

J. R. BATTEN, JR., Assistant Examiner.

1. THE METHOD OF IMPARTING CORROSION-RESISTANCE TO THE SURFACE OF ANORMALLY CORRODIBLE CUPREOUS METAL WHICH COMPRISES CONTACTING SAIDSURFACE WITH THE WORKING FACE OF A RAPIDLY ROTATING RESILIENT RUBBINGELEMENT WHILE MAINTAINING BOTH SAID FACE AND SAID SURFACE IN DRYCONDITION, SAID ELEMENT COMPRISING A POROUS STRUCTURE FORMED FROMORGANIC FIBERS UNIFORMLY PROVIDED AT ITS WORKING FACE AND FOR ASUBSTANTIAL DISTANCE INWARDLY THEREFROM WITH A SUBSTANCE SELECTED FROMTHE CLASS CONSISTING OF ORGANIC COMPOUNDS WHICH ARE CAPABLE OF BEINGBOUND TO CUPREOUS METAL BY CHEMISORPTION AND WHICH INHIBIT THE CORROSIONOF CUPREOUS METAL WHEN APPLIED TO THE SURFACE THEREOF, THE WORKING FACEOF SAID ELEMENT CONTAINING ON THE ORDER OF 0.005 TO 0.1 PART OF SAIDSUBSTANCE PER PART OF FIBER, WHEREBY SAID SUBSTANCE IS FRICTIONALLYTRANSFERRED TO SAID SURFACE TO PROVIDE A UNIFORM COATING HAVING ATHICKNESS SIGNIFICANTLY LESS THAN THE WAVE LENGTH OF VISIBLE LIGHT.